This invention relates to a fault recovery system by unit of wavelength for WDM (wavelength division multiplexing) network.
In order to recover a fault by unit of lightwave path, it is necessary to detect the fault information by unit of lightwave path. In ITU-T G.872 (International Telecommunication Union-T Recommendation G.872), lightwave path to connect between clients is defined as OCH (optical channel), and fault information etc. to be defined in the section of lightwave path is defined as overhead to be assigned to OCH.
In conventional WDM networks, recovering a fault by unit of wavelength-multiplexed signal, i.e. fiber, is generally performed because of its easiness, and recovering a fault by unit of lightwave path is scarcely performed.
One example is a system that when a fault of lightwave path is detected through the overhead of OCH by nodes at the both ends, for the purpose of recovering the fault, the exchange of fault information or switching information from one or both of the nodes to detect the fault is conducted between the nodes at both ends, determining a suitable auxiliary lightwave path to connect between the same nodes, and switching to the auxiliary lightwave path is conducted between the nodes.
In FIG. 1, this system is explained. A WDM network 101 is composed of six nodes 111 to 116. Clients 121 and 122 are connected by a lightwave path 131 at both ends of which nodes 111 and 116 are located. When some fault (141) occurs between the nodes 115 and 116 on the lightwave path 131, various auxiliary lightwave paths, e.g. another path 132 that goes through the same route as the lightwave path 131 but is composed of a wavelength combination different from that of the lightwave path 131 and a lightwave path 133 that goes through another route, can be selected depending on the selection of route and wavelength. The end nodes 111, 116 detecting the fault on the lightwave path exchange in formation each other, determining a suitable auxiliary lightwave path according to the state of fault from the various paths selectable.
Also, another example is a system that a single ring network is assumed as a system for switching by unit of lightwave path and the switching is conducted by nodes at the both ends of lightwave path (Shiragaki et al., IEICE ""98 General Conference, B-10-147).
In FIG. 2, this system is explained. A ring network 201 is composed of six nodes 211 to 216. Clients 221, 222 included here are connected through a lightwave path 231 using a wavelength xcexn and having end nodes 211, 214. When some fault (241) occurs between the nodes 212 and 213 on the lightwave path 231, the nodes 211, 214 switch to a lightwave path 232 using a wavelength xcexn routing the opposite side of the lightwave path 231. In this system, since the selection of auxiliary lightwave path is simplified by limiting the target system to the ring topology, it is advantageous in the simplifying and speed-up of signaling.
In the first conventional system in FIG. 1, provided that the network has a large-scale and complicated composition, the network design and the recovery procedure of signaling must be complicated. Namely, when selecting a suitable auxiliary path in the occurrence of fault, it is impossible to select a suitable route, though not optimum, from the large amount of auxiliary routes in a short time (it is said, several tens milliseconds in basic transmission system) Even if determined in advance, the load of design increases because the number of possible routes increases exponentially to the scale, therefore the entire design has to be widely redesigned every time the network is renewed. In fact, even in the very simple network in FIG. 1, there are many paths selectable. Also, with regard to signaling, a protocol or message format applicable without depending on the composition and scale of network has to be defined taking the extension of network into account. But, probably, it will be very complicated. Further, it is very difficult to offer a stable performance in arbitrary form of network.
In the second conventional system in FIG. 2, the application range is limited to the single ring network. In a network form, which is typical in configuring a ring network, that multiple ring networks are connected each other, when it is applied to lightwave path defined over the multiple ring networks, there occurs a problem similar to that of the system in FIG. 1.
Accordingly, it is an object of the invention to provide a WDM network that even in a complicated or large-scale network system, the load of switching processing at both ends of lightwave path can be reduced.
It is a further object of the invention to provide a WDM network device suitable for the operation of such a WDM network.
According to the invention, a WDM network, comprises:
a lightwave path which connects between clients and each of which is provided with an overhead, and
a sub-network which is defined by dividing the WDM network;
wherein the sub-network includes a partial lightwave path to go through the sub-network, the overhead includes a partial lightwave path supervisory control information region which is terminated at both nodes of the partial lightwave path, and when a fault occurs on a lightwave path, the fault information of partial lightwave path including the position information of fault occurred is added to the partial lightwave path supervisory control information region of the overhead.
According to another aspect of the invention, a WDM network device for composing a connection node between adjacent sub-networks of multiple sub-networks composing a WDM network, comprises:
a partial lightwave path supervisory control information terminating section which monitors a partial lightwave path supervisory control information region in an overhead for a lightwave path to go through the self-node;
a signaling processing section which exchanges information for switching to another node in the sub-network which includes the fault position to determine an auxiliary partial lightwave path when the partial lightwave path supervisory control information terminating section detects that the fault occurred on a partial lightwave path exceeds a given level;
a switching control section which controls the switching of partial lightwave path based on information of the auxiliary partial lightwave path determined; and
a path setting section which switches the partial lightwave path to the auxiliary partial lightwave path by the control of the switching control section.